Fuel rails for supplying fuel to fuel injectors of internal combustion engines are well known. A fuel rail assembly, also referred to herein simply as a fuel rail, is essentially an elongate tubular fuel manifold connected at an inlet end to a fuel supply system and having a plurality of ports for mating in any of various arrangements with a plurality of fuel injectors to be supplied. Typically, a fuel rail assembly includes a plurality of fuel injector sockets in communication with a manifold supply tube, the injectors being inserted into the sockets and held in place in an engine head by bolts securing the fuel rail assembly to the head.
Gasoline fuel injection arrangements may be divided generally into multi-port fuel injection (MPFI), wherein fuel is injected into a runner of an air intake manifold ahead of a cylinder intake valve, and direct injection gasoline (DIG), wherein fuel is injected directly into the combustion chamber of an engine cylinder, typically during or at the end of the compression stroke of the piston. DIG is designed to allow greater control and precision of the fuel charge to the combustion chamber, resulting in better fuel economy and lower emissions. This is accomplished by enabling combustion of an ultra-lean mixture under many operating conditions. DIG is also designed to allow higher compression ratios, delivering higher performance with lower fuel consumption compared to other fuel injection systems. Diesel fuel injection (DID) is also a direct injection type.
For purpose of clarity and brevity, wherever DIG is used herein it should be taken to mean that both DIG and DID, and fuel rail assemblies in accordance with the invention as described below are useful in both DIG and DID engines.
A DIG fuel rail must sustain much higher fuel pressures than a MPFI fuel rail to assure proper injection of fuel into a cylinder having a compressed charge during the compression stroke. DIG fuel rails may be pressurized to about 100 atmospheres or more, for example, whereas MPFI fuel rails must sustain pressures of only about 4 atmospheres. Error proof braze joints are, therefore, necessary for the assembly of fuel rails.
DIG fuel rails further require high precision in the placement of the injector sockets in the fuel supply tube because the spacing and orientation of the sockets along the fuel rail assembly must exactly match the three-dimensional spacing and orientation of the fuel injectors as installed in cylinder ports in the engine. For example, direct injection fuel rail assemblies typically require injector socket to injector socket true positions of less than about 0.5 mm. Braze joints typically require gaps less than 0.05 mm to approach base metal strength. When utilizing the brazing process for producing direct injection fuel rail assemblies both of these requirements must be met. Typical multi-port fuel rail fabrication components and techniques do not meet these requirements making it necessary to find alternate methods.
For example, matched radii with a braze joint have been suggested, where a radius is added to the injector socket to match the radius of the fuel supply tube. This concept requires features to be added to injector sockets and mounting bosses and further requires the use of drawn over mandrel tubing or tubing with improved straightness, which is expensive, labor and cycle time intensive. Accordingly, efforts to form satisfactory DIG fuel rail assemblies by metal forming and welding have not heretofore been successful.
What is needed in the art is an inexpensive, high-precision fuel rail assembly for DIG engine fuel systems.
It is a principal object of the present invention to provide a fuel distribution tube that enables optimization of the true position location of injector sockets as well as improved braze joints.
It is a further object of the invention to enable the use of inexpensive parts and welding methods.